Length adjustable modular screw system

ABSTRACT

A length adjustable modular screw includes a neck assembly and a shank. The neck assembly has proximal and distal ends and includes an expander component and a collet component that are slidably engagable by insertion of the expander component in a through channel of the collet component along a common axis. The length adjustable modular screw also includes a shank suitable for insertion and retention within a bone, the shank including a threaded portion between proximal and distal ends and a socket adapted to coaxially receive at least a portion of the distal end of the neck assembly. The length adjustable modular screw has a length that is selected by splaying at least a portion of the distal end of the engaged expander and collet components of the neck assembly within the socket of the shank.

PRIORITY

The present application is a U.S. patent application which is acontinuation of and claims priority to U.S. patent application Ser. No.16/018,942, filed Jun. 26, 2018, which is a continuation in part of andclaims priority to Patent Cooperation Treaty Patent ApplicationPCT/US2017/048480, filed Aug. 24, 2017, which claims priority to and thebenefit of U.S. Provisional Patent Application No. 62/379,111, filedAug. 24, 2016, each with the title “ADJUSTABLE BONE FIXATION SYSTEMS,”each of which is hereby incorporated by reference in its entirety.

FIELD OF INVENTION

The present invention relates to modular and adjustable assemblies forachieving alignment and fixation of two or more bones or bone segments.In particular embodiments, the invention relates to modular andadjustable assemblies for achieving fixation of bones in the spine.

BACKGROUND

The human skeleton is formed of bones, each bone performing a structuralrole, either individually or collectively with other bones. For example,the spine, which surrounds and protects the spinal cord and associatednerves, provides structure to the body, and enables fluid movement inmany planes. Constructed of essentially twenty-four stacked vertebrae,the spine includes seven cervical vertebrae, twelve thoracic vertebraeand five lumbar vertebrae. A healthy spine is flexible in multipledirections to enable a broad range of physical movement. Intervertebraldisks are disposed between adjacent vertebrae and provide cushioning anddampening to protect the spinal column and nerves in response to thevarious translational and rotational forces associated with body motion.Maintenance of the structural integrity and approximate axial alignmentof the vertebrae is one key to good health.

A clinical subject's spine may be damaged or otherwise compromised inone of many ways. Abnormalities of or damage to the spine include butare not limited to scoliosis (abnormal lateral curvature), kyphosis,excessive lordosis, spondylolisthesis, displaced, degenerative orruptured discs, fractures to one or more vertebral bodies and tumors.These and other possible spinal conditions directly and adversely affectmobility, and also cause moderate to extreme or even debilitating pain,at times accompanied by diminished or lost nerve function.

To ameliorate pain and restore loss of function associated with spinalconditions, a variety of conventional procedures have been developedusing an array of mechanical surgical systems and implants that cansecure two or more vertebrae in a relatively fixed position and canstabilize and straighten spinal deviations along the spinal axis. Astabilization system can be used without fusion treatment of the spine,or in conjunction with fusion treatment of the spine wherein one or morespacing devices is used to replace all or a portion of a vertebral disc.Typically, such discal implants are used together with natural bonecomponents obtained from the clinical subject or a donor source,artificial bone, other biologic components to promote bone growth andfusion between the adjacent vertebral bodies. One or more suchreplacements may be accomplished in a spinal fixation surgery. Thefixation system, with or without fusion components, operates to create asubstantially rigid construct of bone and mechanical hardware thatreplaces damaged or diseased vertebrae and connects them to relativelyhealthier adjacent vertebrae.

Generally, spinal fixation systems involve some mode of stabilizationusing one or more rigid or substantially rigid surgical stabilizationelements, such as a rod or a plate, and means for fastening and securingthe stabilization element to bone. Fastening means can include one ormore bone anchors, such as screws or bolts, assembled with connectorsthat enable engagement with one or more stabilization elements. Theconnectors may include hooks, clamps, cross connectors and otherstructures that engage with one or more of stabilization elements andanchors. These systems of anchor and connector assemblies andstabilization elements are secured to two or more vertebrae and areinterconnected to provide support, encourage alignment or realignment ofthe vertebrae, and to achieve immobilization and fusion.

When spinal fixation surgery is performed from the anterior aspect ofthe clinical subject, it is conventional practice to affix astabilization element in the form of a thin plate, typically formed ofmetal, to adjacent vertebral bodies and secure the plate using anchors,such as screws. When the fixation surgery is performed from theposterior aspect of the clinical subject, it is conventional practice toaffix bone anchors into the vertebral bodies, typically in the pedicle.Multiple levels of adjacent vertebrae may be fixed in this manner.Interconnection of the secured anchors to the stabilization elementcreates a rigid fixation between the adjacent vertebral bodies.

The mode of surgical access may be open, that is, involving a relativelyextensive resection of the soft tissue to plainly expose the vertebraeto be fixated. In some examples, the mode of surgical access may beminimal, wherein less invasive surgical techniques are used to minimizetissue resection. These less invasive approaches have many benefits tothe clinical subject, however, the associated reduction in direct accessand visualization of the vertebral tissue practically means that theanchor implants are difficult to access, grasp and manipulate withinstruments, thus complicating the surgeon's efforts and oftenprolonging the amount of time that the clinical subject is in surgery.

Among the many challenges associated with placement of vertebralstabilization systems is the fact that adjacent vertebrae are typicallynot perfectly aligned. Indeed, along any particular portion of a spine,a series of adjacent vertebrae can deviate laterally a great deal fromthe central axis of the spine. Further, as a result of natural spinalcurvature and any vertebral defects, corresponding portions, such aspedicles, of adjacent vertebra are not in the same plane. In the contextof implanting spinal fixation systems, these variations can beaccommodated to some extent by introducing bends or curves in thesubstantially rigid stabilization element(s) used for fixation. But ininstances where the therapeutic benefit is obtained by realigningadjacent vertebrae, adjustment of the curvature of the stabilizationelement(s) is not a completely satisfactory solution. Accordingly, it istypically the case that the surgeon and surgical team must manipulatethe spine and the system instruments in an attempt to align the securedanchors for attachment to a stabilization element. Often, the extent ofnonalignment, both in terms of longitudinal and vertical planarpositions of vertebrae along the spine, can cause failure of one or moreof the system components, extend surgery, cause damage to the clinicalsubject's spine, and ultimately lead to a less than desirable clinicaloutcome. The challenges of access in minimally invasive procedures cancompound the difficulties associated with non-aligned vertebral bodies.

Attempts have been made in the design of spinal fixation systems toaddress variability of spinal anatomy, such as those variationsdescribed above. In many examples of conventional systems, anchors areadapted to achieve a range of variability in positioning based onpivotal rotation of the anchor such that the axis of the secured anchorrelative to the stabilization element can be varied. These are referredto as poly-axial and uni-axial anchors. They are useful in particularfor facilitating attachment of a stabilization element to two or morevertebrae that are not aligned along the spinal axis. There are otherexamples of systems that are adapted with features that facilitateengagement of non-axially aligned vertebrae. But there are noconventional systems suitable for accommodating the variability in therelative height of adjacent vertebrae, wherein corresponding portions ofadjacent vertebrae are not on the same plane. Further, there are noconventional systems that allow the surgeon the option to install boneanchors into the bone and then select from a suite of modular anchorcomponents to achieve an optimized system for fixation that avoids orminimizes the problems associated with anatomical variations in thespine. Beyond the spine, such as for other bones and bone fragments inthe body, there are likewise no systems that provide either or bothmodularity and length adjustability options in the fixation or reductionof bones and bone fragments.

To address the above-described challenges, there is need for boneanchors and other implants that meet or exceed the functionality ofconventional anchors while also providing adjustability, and ideally,modularity, to address the height variability of vertebral bodies thatdo not share a common plane. Thus, what is needed, for example in thecontext of the spine, is a fixation system that includes one or moreanchors that are capable of mono-, uni-, and poly-axial positioning andallow substantial vertical travel between the distal attachment point inthe bone and the proximal position of a stabilization element, and arecapable of locking to avoid further vertical travel after the systemimplantation is completed. Such an anchor would enable simplifiedattachment of adjacent anchors to a stabilization element by reducingthe extent of height variability of adjacent anchors, thereby avoidingmany of the challenges faced in the surgical setting.

SUMMARY

The present invention describes various exemplary systems and methods ofinstallation of one or more anchors and stabilization elements that areadapted for height adjustability during spinal fixation surgery. Thedisclosure is directed in various embodiments, both described andcontemplated, to assemblies, subassemblies and modular components andtheir methods of use and installation for achieving adjustable fixationand/or reduction of bones and bone fragments.

Provided in various embodiments is a length adjustable modular anchorsystem and methods of use thereof for engagement with a bone. In anexemplary embodiment, the length adjustable modular anchor systemincludes a length adjustable modular screw that includes a neck assemblyand a shank.

In various embodiments, the disclosure provides a length adjustablemodular screw that includes a neck assembly that has proximal and distalends and includes an expander component and a collet component that areslidably engagable by insertion of the expander component in a throughchannel of the collet component along a common axis. The lengthadjustable modular screw also includes a shank suitable for insertionand retention within a bone, the shank including a threaded portionbetween its proximal and distal ends and a socket adapted to coaxiallyreceive at least a portion of the distal end of the neck assembly. Thelength adjustable modular screw has a length that is selected bysplaying at least a portion of the distal end of the engaged expanderand neck components of the neck assembly within the socket of the shank.The length adjustable modular screw is one of monoaxial, uniaxial, andpoly-axial.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the disclosed inventions will now be discussedwith reference to the appended drawings. These drawings merely depictrepresentative embodiments and are not limiting in scope.

FIG. 1 shows a front plan view (a.) and alternate perspective views (b.and c.) of a length adjustable modular anchor system according to thedisclosure;

FIG. 2 shows exploded (a.) and assembled (b.) perspective views of theneck assembly of the length adjustable modular anchor system shown inFIG. 1 ;

FIG. 3 shows a front plan view (a.), an exploded perspective view (b.)and a close up perspective (c.) view of the length adjustable modularanchor system shown in FIG. 1 ;

FIG. 4 shows on the left alternate top perspective (a.), side plan (b.),and partial close up side plan (c.) views of an expander component ofthe neck assembly shown in FIG. 2 , and on the right alternate topperspective (d.), bottom perspective (e.), and side cross sectional (f)views of a collet component of the neck assembly shown in FIG. 2 ;

FIG. 5 shows an alternate side plan (b.), top, (a.) perspective (e.),and alternate side cross sectional (c. and d.) views of a shankcomponent of the length adjustable modular anchor system 10 shown inFIG. 1 ;

FIG. 6 shows on the top a top plan view (a.), and on the bottom sideplan (b.) and cross sectional (c.) views of the length adjustablemodular anchor system 10 shown in FIG. 1 , and a top plan view (f.),side plan (d.) and cross sectional (e.) views of an alternate embodimentof a length adjustable modular anchor system 10 that includes aretaining housing 20, a compression washer 30 and a locking element 40according to the disclosure; and

FIG. 7 shows each, individually in alternate views, the retaininghousing 20 (a.), a compression washer 30 (top perspective, b., andbottom perspective, c.), locking element 40 (d.), and protuberance 570(e.).

Table of Reference Numerals length adjustable modular anchor system 10through slot 452 retaining housing 20 interference enhancer 454 (e.g.,compression washer 30 (e.g., cap) groove/furrow/ rib) locking element 40(e.g., set screw) leg 456 rod (not shown) compression element 460complementary taper 462 length adjustable modular screw 100 shapedrecess 470 neck assembly 200 recess proximal stop 472 recess distal stop474 expander component 300 outer surface 480 head 310 (hemispherical)chamfered corners 482 foot 320 collet cross sectional shape 490 (e.g.,square) foot cross sectional shape 322 pin 330 shank 500 threadedportion 510 taper 332 proximal end 520 extension 334 proximal aperture522 circumferential flange 340 proximal thread zone 524 flange generallyplanar surface 345 distal end 530 flange taper 347 distal tip 532 detentregion 350 distal thread zone 534 drive recess 360 (hex) socket 540 pin330 socket cross sectional shape 542 (e.g., sq/cyl) cross sectionalshape 370 e.g., (sq/cyl) chamfered sidewall 544 wall 550 colletcomponent 400 wall aperture 560, 560′ proximal end 410 protuberance 570,570′ distal end 420 floor 580 through channel 430 floor taper 582 innerwall 431 diameter 590 (e.g., straight, tapered, step down) inner wallcross sectional shape 432 major diameter 592 (cylindrical) minordiameter 594 seat 440 (hemispherical) cannula 596 seat recess 441 flange598 seat recess cross sectional shape 442 e.g., (sq/cyl) collet 450

DETAILED DESCRIPTION

This Detailed Description describes exemplary embodiments in accordancewith the general inventive concepts and is not intended to limit thescope of the invention in any way. Indeed, the invention as described inthe specification is broader than and unlimited by the exemplaryembodiments set forth herein, and the terms used herein have their fullordinary meaning.

The general inventive concepts will now be described with occasionalreference to the exemplary embodiments of the invention. This generalinventive concept may, however, be embodied in different forms andshould not be construed as limited to the embodiments set forth herein.Rather, these embodiments are provided so that this disclosure will bethorough and complete, and will fully convey the scope of the inventiveconcepts to those skilled in the art.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art encompassing the general inventive concepts. The terminology setforth in this detailed description is for describing particularembodiments only and is not intended to be limiting of the generalinventive concepts. As used in this detailed description and theappended claims, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise.

The term “proximal” as used in connection with any object refers to theportion of the object that is closest to the operator of the object (orsome other stated reference point), and the term “distal” refers to theportion of the object that is farthest from the operator of the object(or some other stated reference point). A “clinical subject” refers to ahuman or other animal who is the subject of treatment with a bonefixation or reduction device in accordance with the disclosure. Withrespect to any references herein that may be made relative to a clinicalsubject, the term “cephalad” indicates a direction toward the head ofthe clinical subject, and the term “caudad” indicates a direction towardthe feet of the clinical subject. The term “posterior” indicates adirection toward the back of the clinical subject, the term “anterior”indicates a direction toward the front of the clinical subject, and theterm “lateral” indicates a direction toward a side of the clinicalsubject.

The term “height” as used specifically herein pertains to references tothe spine of a clinical subject and refers to the relative position ofone or both of vertebrae and anchors along adjacent portions of thespine. Likewise, the terms “vertical” and “vertical adjustment” relateto the relative height variations and adjustments thereof with respectto one or both of vertebrae and anchors along adjacent portions or thelength of the spine in the context of a clinical subject in a proneposition wherein a length adjustment to an anchor would be in a verticaldimension from anterior to posterior. These descriptors are not intendedto be limiting with respect to embodiments of the modular adjustableassemblies, subassemblies and components according to the instantinvention that are useful outside of the spine and may more genericallybe substituted with alternate descriptors including “length” and “lengthadjustment” where orientation of the clinical subject or body part andbones and implants vary.

As used herein in the described and illustrated embodiments, the termanchor typically refers to the screw component of an anchor assembly orsubassembly, and the term anchor assembly refers to the screw componenttogether with attachment features, such as a retaining housing (aconventional tulip head) or other type of attachment device, and one ormore of compression washers and set screws, and optionally additionalfixation components. Subassemblies also refer to the modular componentsof the screw, such as, for example, the shank and head portions andsubassemblies of these. More generically, anchor components,subassemblies and assemblies can be adapted to include features suitablefor use with any bones in a clinical subject, wherein the modular andadjustable features are as described and claimed herein.

Unless otherwise indicated, all numbers expressing quantities ofmaterials, properties such as length, diameter, and so forth as used inthe specification and claims are to be understood as being modified inall instances by the term “about.” Accordingly, unless otherwiseindicated, the numerical properties set forth in the specification andclaims are approximations that may vary depending on the suitableproperties sought to be obtained in embodiments of the presentinvention. Notwithstanding that the numerical ranges and parameterssetting forth the broad scope of the general inventive concepts areapproximations, the numerical values set forth in the specific examplesare reported as precisely as possible. Any numerical values, however,inherently contain certain errors necessarily resulting from error foundin their respective measurements.

Referring now to the drawings, an embodiment of a modular and lengthadjustable modular anchor system 10 for securing a bone stabilizationelement, such as a spinal stabilization rod, to a bone is depicted inFIG. 1 -FIG. 6 . As further described herein, the length adjustablemodular anchor system 10 includes a length adjustable modular screw 100which can be varied in length.

In accordance with the depicted embodiments, the length adjustablemodular screw 100 is assembled to provide a construct that resembles aconvention screw that includes a head 310 portion including at aproximal end 410 a hemispherical screw head and a separate threadedshank 500 portion including at a distal end a threaded shank 500. Inaccordance with the disclosure, the length adjustable modular screw 100components are adapted for interconnection along a common elongate axisand capable of vertical displacement to achieve fixed or variable lengthwhen implanted in a bone. In conventional pedicle screw anchors,pressure from the rod locked into the retaining housing 20 (tulip head)by a threaded nut results in displacement of the compression washer 30within the tulip head 20 and compression on the head of the screwthereby transferring compressive force onto the screw, fixing it intoplace within the tulip head 20 and preventing any axial rotation (foruni- and poly-axial assemblies). FIG. 6 provides an example of such asystem that includes an embodiment of a length adjustable modular screw100 according to the disclosure. In use, the compressive force employedto lock a rod to a conventional screw also serves to lock the lengthadjustable modular screw 100 embodiments according to this disclosure,thereby fixing the vertical position selected by the surgeon.

Length Adjustable Modular Anchor System

Provided in alternate embodiments is a length adjustable modular anchorsystem 10 for engagement with a bone. In one embodiment, as shown inFIG. 1 , the length adjustable modular anchor system 10 includes alength adjustable modular screw 100 that includes a neck assembly 200and a shank 500. Referring now to FIG. 2 , the neck assembly 200includes an expander component 300 and a collet component 400. Asassembled, a portion of the expander component 300 is insertable withina through channel 430 in the collet component 400 along a common axis,as shown in FIG. 2 . The collet component 400 through channel 430originates within the seat 440 and extends through the distal end 420 ofthe collet 450. When engaged, the head 310 of the expander component 300contacts the seat of the collet component 400 and the pin 330 is passedthrough the through channel 430. In some embodiments, as depicted in thedrawings, the expander component pin 330 includes an extension 334 thatextends beyond the distal end 420 of the collet 450. In otherembodiments, the expander component pin 330 may lack such an extension334 and thus, the pin 330 may not extend beyond the distal end 420 ofthe collet 450.

The expander component 300 and the collet component 400 are engagable ineach of open, mated and compressed configurations. In the openconfiguration, the expander component 300 and the collet component 400are engaged without the head 310 contacting the seat 440 and the pin 330of the expander component 300 is coaxially engaged with and onlypartially inserted in the through channel 430 of the collet component400 and the expander and collet components 300, 400 are freely movablealong the common axis.

In the mated configuration, as shown in FIG. 3 (center image), the head310 is contacting the seat 440 and the head 310 of the expandercomponent 300 and the seat 440 of the collet component 400 are mated butnot compressed, and the pin 330 of the expander component 300 is fullyinserted in the through channel 430 of the collet component 400. In eachof the open and the mated configurations, the collet 450 is not splayed.In the compressed configuration, the expander component 300 and thecollet component 400 are mated and the head 310 and the seat 440 arecontacted and in compression, and the collet 450 is splayed such that ithas an overall greater diameter 590 than in its non-splayedconfiguration. Each of the expander and collet components 300, 400include cooperating features that are compressible together to splay thecollet 450.

Referring now to FIG. 4 , left, the expander component 300 includes ahead 310 at a proximal end and a pin 330 that extends from the head 310at a distal end. Referring again to FIG. 4 , right, the collet component400 includes at a proximal end 410 a seat 440 that is matable with thehead 310 of the expander component 300, and at a distal end 420 a collet450 that extends from the seat 440. In some embodiments, each of thehead 310 of the expander component 300 and the seat 440 of the colletcomponent 400 are generally hemispherical in shape and mated 220 to forma generally spherical head 310, the mated 220 pin 330 and collet 450features forming a generally rod-shaped extension from the sphere. Ofcourse, it will be appreciated that in some embodiments, the head 310and seat 440 features may be other than hemispherical. As depicted, theexpander component 300 has a head 310 that is generally hemisphericaland includes a flat at its apex that includes a drive recess 360 forengaging a driver. Any suitable shaped drive recess 360 may be employedfor engagement with any of a variety of drivers.

As shown in the drawings, in some embodiments the head 310 of theexpander component 300 includes a foot 320 having a generally squarecross sectional shape, and the seat 440 of the collet component 400includes a complementary seat recess 441 having a generally square crosssectional shape for receiving the foot 320 of the extender component300.

In the various embodiments, the collet 450 includes at least one throughslot 452 oriented parallel to the common axis and along at least aportion of the collet 450 through the distal end 420. And in someembodiments the collet 450 includes a plurality of through slots 452arranged circumferentially around the collet 450 and extending along atleast a portion of the length of the collet 450 and through the distalend 420. As shown in the drawings, for example FIG. 4 , the collet 450includes four through slots 452. In the depicted embodiment, the collet450 has a generally square cross sectional shape 490, and each of thethrough slots 452 are arranged, respectively, on a side of the collet450 to form four legs. As depicted, the collet 450 has chamfered corners482 and generally planar sides on its outer surface. And the collet 450includes on its outer surface at its distal end 420 an array ofinterference enhancers 454. As shown, the interference enhancers 454include a knurled texture. In other embodiments, the feature may includeother textural elements, or may include one or more furrows, divots orridges. The interference enhancers 454 may enhance the contact with thewall 550 of the socket 540 within the shank 500 when the collet 450 issplayed. And the interference enhancers 454 may also enhance theflexibility of the shank 500 for splaying. It will be appreciated thatin some embodiments the collet 450 lacks such interference enhancers454. And as shown in the depicted embodiment, the collet 450 includes atits distal end 420 on each leg 456 and within the through channel 430 acompression element 460 that is generally block shaped with a proximallyoriented taper or angle.

It will be appreciated that a variety of conventional features ofcollets 450 are known in the art and may be selected to facilitatelocking and compression and/or frictional engagement between a collet450 and engaged anchor components. In some instances, variations in thethickness of walls 550 of one or more components can be employed toachieve compressive engagement. In other examples, collet 450 featuresmay include tapers along the length of engaging components. It will beunderstood that the features described herein are intended to benon-limiting and other features of collets 450 known in the art may beused to achieve the inventive modular and adjustable anchors inaccordance with the invention.

In some embodiments, at least one of the expander component 300 and thecollet component 400 includes a locking feature that is engagable whenthe head 310 of the expander component 300 and the seat 440 of thecollet component 400 are mated 220. In some such embodiments, as isshown, for example in FIG. 2 , the locking feature includes acircumferential flange 340 on the pin 330 of the expander component 300that interferes with the distal end 420 of the collet 450 when theexpander and collet components 300, 400 are in the mated 220 arrangementto limit displacement of the expander component 300. As shown in thedrawings, the circumferential flange 340 is located at a position thatis between the proximal and distal ends 410, 420 and includes agenerally planar surface 345 on a proximal edge which abuts a taper 347that is angled toward the common axis from proximal to distal to form agenerally conical taper shape. And as shown, the pin 330 has a diameterat its proximal end 410 that is greater than the diameter at its distalend 420.

In some embodiments, the pin 330 of the expander component 300 alsoincludes a detent region 350, which is shown in FIG. 2 . As depicted,the detent region 350 has a diameter that is approximately the same asthe diameter of the pin 330 at the distal end 420. And as depicted, thedetent region 350 is abutted at its proximal end by a taper 332 that isangled toward the common axis from proximal to distal to form agenerally conical shape and abuts at its distal end the generally planarsurface 345 of the circumferential flange 340. Referring again to FIG. 4, the collet component 400 includes at least one compression element 460within the collet 450 through channel 430 for contacting the taper 332of the pin 330.

As shown in the drawings, for example in FIG. 2 , the at least onecompression element 460 of the collet 450 is engagable within the detentregion 350 of the pin 330 of the expander component 300 when theexpander and collet components 300, 400 are mated 220. In variousembodiments, the compression element 460 extends into the collet 450through channel 430, and has a shape that is one of angled, radiused andsquared. In various embodiments, the compression element 460 may beformed continuously and interrupted only by the through slots 452, andmay be dome shaped, may have planer circumferential flange 340 shape,may include one or more conical or beveled edges, and may be wedgeshaped. And there may be more than one compression element 460 arrangedalong the length of the through channel 430.

Referring again to the drawings, for example FIG. 4 , the pin 330 has across sectional shape 370 that is generally cylindrical and the throughchannel 430 of the collet component 400 has an inner wall 431 with aninner wall cross sectional shape 432 that is cylindrical. It will beappreciated that in other embodiments, each of the pin 330 crosssectional shape 370 and the inner wall cross sectional shape 432 may beother than cylindrical.

It will be appreciated that in other embodiments, the expander component300 and the collet component 400 may include features that engage tomate and compress that are located at positions other than as shown inthe drawings. For example, one or more of the circumferential flange 340and the detent region 350 and the taper 332 on the pin 330 may bepositioned more proximally or more distally, and the pin 330 may notinclude an extension beyond one or more of the circumferential flange340 and the detent region 350 and the taper 332. Likewise, one or moreof compression elements 460 may be positioned more proximally or moredistally within the through channel 430 of the collet component 400.

As shown in the drawings, the expander component 300 pin 330 includes aconical taper 332 between the detent region 350 and a proximal portionof the pin 330, wherein the one or more compression elements 460 of thecollet 450 comprises a complementary taper 462, which complementarytaper 462, when pressed against the detent region 350 proximal taper 332of the pin 330, splays the collet 450.

Referring now to FIG. 1 , FIG. 3 , and FIG. 5 , the length adjustablemodular anchor system 10 also includes a shank 500 that includes athreaded portion 510 between proximal and distal ends 520, 530. Asshown, the shank 500 includes at its distal end 530 a distal tip 532that may be bulleted (not shown) and is suitable for penetrating bone.The shank 500 includes at its proximal end 520 an aperture that is incommunication with a socket 540. The socket 540 extends within the shank500 along a length from the proximal end 520 toward the distal end 530and is adapted for receiving at least a portion of the collet 450 of theneck assembly 200. When the length adjustable modular anchor system 10is assembled, the neck assembly 200 is adjustably engagable within theshank 500 to achieve variable length of the length adjustable modularscrew 100.

In the various embodiments, the threaded portion 510 of the shank 500may be continuous from the proximal to the distal ends 520, 530, orthere may be a gap at either end that lacks threading, or a gap alongthe length that lacks threading. In the various embodiments, the shank500 includes at least a major and a minor diameter 592, 594, the minordiameter 594 defined by the outer surface of the shank 500 wall 550excluding the threads, and the major diameter 592 defined by thethreads. In some embodiments, one or both of the major and minordiameters 592, 594 may be straight or may be tapered. In someembodiments, there may be a step down from proximal toward distal suchthat there may be more than one major diameter 592 and/or more than oneminor diameter 594. In some embodiments, at least a portion of thelength of the shank 500 may taper from proximal to distal eithercontinuously or may taper in a stepped down manner. In some embodiments,the threading may vary to provide a proximal thread zone 524 that isdifferent from a distal thread zone 534.

Referring again to the drawings, the depicted collet has a crosssectional shape 490 that is generally square and the socket 540 of theshank 500 has a socket cross sectional shape 542 that is square, each ofthe collet 450 and the socket 540 including chamfered corners 482 andchamfered sidewalls 544, respectively. It will be appreciated that inother embodiments, each of the collet cross sectional shape 490 and thesocket cross sectional shape 542 may be other than square and may becylindrical.

As shown, for example in FIG. 3 , the shank 500 includes at least one,and as depicted, includes two wall apertures 560, 560′ that are adaptedfor receiving a protuberance 570 through each for engagement with theneck assembly 200, as described further below. It will be appreciatedthat in some embodiments, protuberance 570 may be integrated with theshank 500. And while the drawings show the pin 330 insertable in anaperture 560, 560′ through a flange 598 on the shank 500, in someembodiments, the shank 500 may lack a flange 598.

In accordance with some embodiments, the length adjustable modular screw100 further includes at least one locking feature on at least one of theneck assembly 200 and the shank 500 that engages to retain the neckassembly 200 within the shank socket 540. Referring now to FIG. 3 andFIG. 4 , in some embodiments, the locking feature includes a shapedrecess 470 along at least a portion of the length of the colletcomponent 400 and a complementary protuberance 570 situated at theproximal end 520 of the shank 500. The protuberance 570 extends into theshank socket 540 and is engagable with the shaped recess 470 of thecollet component 400. The locking feature prevents pull out of the neckassembly 200 from the shank socket 540. The locking feature also limitsrotational motion of the neck assembly 200 within the socket 540. Asshown, the shaped recess 470 has a generally elliptical shape and iselongate from the proximal 410 and towards the distal end 420 of thecollet component 400. The shaped recess 470 includes proximal and distalstops 472, 474. It will be appreciated that other shapes for the shapedrecess 470 may be employed, and the shaped recess 470 may have a longeror shorter length along the collet 450.

Other features of the neck assembly 200 engage with the shank 500 tofurther stabilize the engagement. Referring again to the drawings, theexpander component pin 330 includes an extension 334 at its distal end,and the shank socket 540 includes a floor 580 and cannula 596 extendingfrom the floor 580 towards the distal end 530. The distal end 420 of thecollet 450 contacts the floor 580 to limit the distal passage of theneck assembly 200 within the socket 540, and the cannula 596 is adaptedto receive the expander component 300 extension which aids instabilizing against off axis motion of the neck assembly 200 relative tothe shank 500. In some embodiments, the length of each of the extensionof the expander component 300 and the shaped recess 470 of the collet450 are selected such that when the neck assembly 200 is displacedproximally to the limit of the distal stop 474, the extension isretained in the cannula 596 to maximize off axis stabilization togetherwith restriction on axis pull out. As is shown in the drawings, thefloor 580 of the shank 500 has a generally conical floor taper 582. Insome embodiments, the floor 580 may have another shape, and may beplanar, or have a spherical contour or another shape.

It will be appreciated that in alternate embodiments different oradditional engagement features may be used that achieve the fixedengagement between subcomponents. Such engagement is useful to enabletorsional engagement and actuation, such as with a driving tool, of oneor more components while preventing other components from experiencingtorsional force. Likewise, it is advantageous to employ engagementfeatures that serve as stops to prevent disengagement of components bythe application of shear force, such as pull out of axially alignedcomponents.

Referring again to FIG. 6 , an embodiment of a length adjustable modularanchor system 10 for engagement with a bone is shown. The lengthadjustable modular anchor system 10 includes a length adjustable modularscrew 100 comprising a neck assembly 200 and a shank 500, a rod (notshown) and at least one retaining housing 20 and a locking element 40for engaging and securing the length adjustable modular screw 100 andthe surgical rod. Optionally, the length adjustable modular anchorsystem 10 also includes one or more compression washers 30 forengagement between the rod and a bone anchor. In use, one or more thanone length adjustable modular anchor system 10 may be employed togetherwith one or more conventional bone anchors, and additional componentsincluding surgical rods (or other stabilizing members, not shown),retaining housings 20, locking elements 40 and optional components suchas compression washers 30. Arrays of anchors and rods may be used forexample to stabilize adjacent vertebral bodies which may includeplacement of up to four or more anchors, two each within pedicles ofadjacent vertebral bodies and engagement of a spinal rod to each of thepair of adjacent anchors to confer stabilization along the length of thespine.

Also provided according to the disclosure is a surgical method forinstalling a bone anchor system for spinal fixation. According to themethod, the steps include in some embodiments selecting each of two ormore bone anchors, at least one of which bone anchors is a lengthadjustable modular anchor system 10 that includes a neck assembly 200and a shank 500, as described herein above, and at least one spinal roddefining a longitudinal axis, and two or more retaining housings 20 forengaging and securing a bone anchor and a surgical rod, and two or morelocking elements 40 for securing a rod to a bone anchor, and optionally,one or more compression washers 30 for engagement between a rod and abone anchor. Further according to the method, the steps include, eitherbefore or after seating the neck assembly 200 in a retaining housing 20,assembling a length adjustable modular screw 100 system.

The steps for assembling a length adjustable modular screw 100 systeminclude first engaging the expander and collet components 300, 400 ofthe neck assembly 200 into one of open and mated 220 engagement, andinserting the neck assembly 200 into the shank 500 socket 540, thencontacting the distal tip 532 of the shank 500 with a bone. Thereafter,using a suitable driver, engaging the drive recess 360 of the neckassembly 200 to compress the expander and collet components 300, 400 andsplay the collet 450. Thereafter, under continued compression, drivingthe threaded portion 510 of the shank 500 into a bone. Once the shank500 is inserted to the desired depth in bone, the steps includereleasing the drive compression on the drive recess 360 of the neckassembly 200 to thereby relieve the collet 450 from being splayed andthereby allowing translation of the neck assembly 200 within the shank500.

Thereafter, either before or after provisionally securing a surgical rodinto the retaining housing 20, the vertical height (length) of thelength adjustable modular anchor system 10 may be adjusted by slidingthe neck assembly 200 along the common axis within the socket 540 of theshank 500. Once the desired length and vertical height relative toadjacent anatomy and/or other anchors or implants is selected, themethod includes tightening the fixation element within the retaininghousing 20 to compress the rod against the neck assembly 200 and todrive the expander component 300 and the collet component 400 intocompressed engagement to splay the collet 450 within the socket 540 ofthe shank 500.

In some embodiments of the surgical method, the length adjustablemodular anchor system 10 is fully assembled prior to engagement of thethreaded portion 510 of the shank 500 with bone. In yet otherembodiments, the length adjustable modular anchor system 10 is providedpre-assembled. And in yet other embodiments, at least the neck assembly200 of the length adjustable modular anchor system 10 is providedpre-assembled with a retaining housing 20.

In some embodiments, the length adjustable modular screw 100 can beadjusted within a displacement range between zero mm to 20 mm, and moreparticularly 0 mm to 10 mm, including fractional increments therein,including 0.1, 0.2, 0.3, 0.4, 0.5, 1.0, 1.5, 2.0, and 2.5 up to andthrough 20.0 mm. Of course, other increments and ranges of travel arepossible, and implementation thereof is well within the skill in theart.

It will be appreciated that in each of the various embodiments accordingto the invention, more than one length adjustable modular screw may beprovided that are of varying lengths and therefore allow for an expandedrange of length adaptability. Whether the length adjustable modularscrew components are of fixed length or offered in ranges of lengths,such possible embodiments are particularly advantageous in that theyprovide options in some embodiments for providing preassembled bottomand top loading anchor assemblies, as well as anchor assemblies andsubassemblies that may be assembled partially by the manufacturer orpartially or completely by the surgeon, providing a range of options forachieving maximal flexibility in the surgical setting.

As described herein in accordance with the depicted embodiments, thecomponents of the length adjustable modular screw 100 assembly thatachieve locking of the length adjustable modular screw 100 to a rod canalso actuate the collet 450 locking mechanism for fixing the neckassembly 200 of the length adjustable modular anchor system 10 to theshank 500 and optionally fixing the vertical position of the lengthadjustable modular screw 100 relative to the vertebra and the fixationsystem elements. Of course, in other embodiments, the means of achievinglocking may be other than compression by the rod, and in yet otherembodiments the locking means may be the same but the specific elements,such as the locking element 40, rod and compression washer 30, may bevaried.

Reference is made herein to fixation systems that include in thedepicted embodiments anchors in the form of vertebral pedicle screws,and stabilization elements in the form of one or more surgical rods. Itwill be appreciated by those skilled in the art that the spine is butone example of a bone or bone system that may be the object of surgicalcorrection, and thus, pedicle screws and rods are mere examples of thebone anchor, and vertebral stabilization system components contemplatedherein. In other examples, anchors may be screws for engagement with atether or other tensioning means, or with one or more plates or rods orcombinations of these. And anchors and systems described herein may besuitable for other bones and bone systems in the body. Moreover, it willbe appreciated that the mechanisms for adjustment of anchor length canbe adapted for use with other anchor and fixation and stabilizationelements used in orthopedic applications in the spine or in other partsof the body.

In one example, spinal rods may be made adjustable according to thefeatures disclosed herein to enable tuned adjustment of rod length atthe time of implantation or subsequently as spinal healing and oradjustment takes place, such as for adjustment of rod length inconnection with scoliosis treatment. In yet other examples, adjustableanchors may be employed in the reduction or fixation of other bones,such as bones of the hand, or of the foot or in other locations whereadjustment of the length of an anchor or other fixation element isdesirable. One such example would be incorporation of adjustabilityfeatures disclosed herein in dual threaded headless screws or screws,rods or pins with other head and threading configurations that are usedfor interconnecting and reducing fractured bone fragments or adjacentbones. Such anchors adapted according to the instant disclosure wouldenable tuned adjustment of implant length to accommodate anatomicalvariations in a clinical subject and achieve optimized anchor placement.

The invention is directed in various aspects to a system includingassemblies and subassemblies, components including anchors and anchorcomponents adapted for attachment to a bony structure of a clinicalsubject. In an exemplary embodiment wherein the use is in connectionwith fixation of the spine, wherein one, two or more such anchors in theform of screws are affixed to bones, for example, vertebral structuressuch as the pedicle, and each anchor is connected to a stabilizer suchas a surgical rod that is inserted between the anchors. The anchors arenovel in many respects owing to their modular nature and thus theoptions to provide the anchors in modular, sub-assembled and assembledforms provide a broad array of choices for the surgeon in devising theoptimal surgical fixation plan.

In use by a surgeon, installation of the inventive components of theexemplary bone anchor system for spinal fixation described aboveincludes: selecting two or more bone anchor assemblies or subassemblies,including assemblies and subassemblies selected from pre-assembled andtop and bottom loading forms, wherein at least one anchor assemblyincludes an length adjustable modular screw; selecting a stabilizationelement; using a suitable driver to drive each of two or more anchors oranchor subassemblies into fixed engagement with corresponding vertebrae,wherein at least one anchor or anchor subassembly includes or is adaptedto engage with modular components that allow length adjustability,including translation along the vertical axis of the anchor, so as toenable selection of the anchor length by the surgeon; engaging aproximal portion of the modular adjustable anchor, such modular portionselected from a pre-assembled or modular screw head and engagement seat,to provide a means to introduce the stabilization element intoengagement with the anchor; optionally incrementally adjusting thelength of the anchor so as to achieve engagement of the stabilizationelement in the anchor; sliding the stabilization element into placewithin the anchor; introducing a fixation element to at leasttemporarily fix the stabilization element within the anchor; optionally,adjusting at least the vertical position of the anchor to optimize itsheight orientation relative to the stabilization element and adjacentanchors; tightening the fixation element to compress the stabilizationelement within the anchor assembly, thereby fixedly engaging the modularcomponents of the anchor so as to lock the position of the anchor andalso lock its engagement with the stabilization element. This process isrepeated for each adjustable anchor in the system, and conventionalmethods are used with conventional anchors.

It will be appreciated by one of skill in the art that the lengthadjustable modular screw described herein may be employed withcomponents of a conventional spinal stabilization system, and may beused on a single vertebra, or traversing two or more vertebra, and maybe used in conjunction with fusion or non-fusion treatment of the spine.Of course, in various examples, the anchors may be employed in isolationor in systems that include two or more anchors, connectors andstabilization elements, and the anchors may be deployed other than alongthe spinal axis. Thus, in other examples of use, two or more anchors maybe used to secure one or more stabilization elements that extend eitherlaterally or from an anterior to posterior aspect to traverse avertebral body, or that wrap around one or more vertebral bodies, orcombinations of these. And of course it will be appreciated that in someexamples the assemblies and subassemblies, components, including anchorsand anchor components, may be used in bones of the body other than thespine, and as such may be used individually, as a plurality, or incombination with other devices, and combinations of these.

What is claimed:
 1. A surgical method for installing a bone anchorsystem for spinal fixation, comprising: (i) selecting each of: (a) alength adjustable modular screw comprising: a neck assembly thatincludes an expander component and a collet component, the neck assemblyhaving proximal and distal ends and including expander and colletcomponents that are slidably engagable by insertion of the expandercomponent in a through channel of the collet component along a commonaxis, and a shank suitable for insertion and retention within a bone,the shank including a threaded portion between its proximal and distalends and a socket adapted to coaxially receive at least a portion of thedistal end of the neck assembly, wherein the length adjustable modularscrew has a length that is selected by splaying at least a portion ofthe distal end of the engaged expander and collet components of the neckassembly within the socket of the shank, wherein the length adjustablemodular screw is one of monoaxial, uniaxial, and poly-axial; and (b) atleast one spinal rod defining a longitudinal axis; (c) two or moreretaining housings, each retaining housing adapted for engaging andsecuring a bone anchor and the at least one spinal rod; (d) two or morelocking elements, each locking element adapted for securing the at leastone spinal rod to a bone anchor (ii) either before or after seating theneck assembly in a retaining housing, assembling a length adjustablemodular screw, comprising the steps of: (a) engaging the components ofthe neck assembly into engagement, and inserting the neck assembly intothe socket of the shank, (b) contacting the distal end of the shank witha bone, (c) with a suitable driver, engaging a drive recess of the neckassembly to splay at least a portion of the distal end of the engagedexpander and collet components of the neck assembly within the socket ofthe shank, (d) driving the threaded portion of the shank into the bone,(e) either before or after provisionally securing the at least onespinal rod into the retaining housing, adjusting the length of thelength adjustable modular screw by sliding the neck assembly along thecommon axis within the socket of the shank; tightening one of thelocking elements within the retaining housing to compress the at leastone spinal rod against the neck assembly and to lock the neck assemblywithin the socket of the shank.
 2. The surgical method according toclaim 1, wherein the length adjustable modular anchor system is fullyassembled prior to engagement of the threaded portion of the shank withthe bone.
 3. The surgical method according to claim 1, wherein thelength adjustable modular anchor system is provided pre-assembled. 4.The surgical method according to claim 1, wherein the first expandercomponent of the neck assembly includes an extension that extends beyondthe distal end of the collet component of the neck assembly.
 5. Thesurgical method according to claim 1, wherein the expander and colletelongate components are matable at their proximal ends when the expandercomponent is inserted in the through channel of the collet component. 6.The surgical method according to claim 1, wherein the expander componentcomprises a head at its proximal end and the collet component comprisesa seat at its proximal end, wherein the head and seat, when mated form agenerally spherical head on the neck assembly.